Asthma is a chronic inflammatory condition affecting the lungs. It is characterized by reversible or at least partially reversible constrictions of the bronchi in the lungs. Bronchi are muscular tubes that carry air throughout the lungs, transporting it to and from smaller airway branches called bronchioles.

With asthma, the walls of the bronchi are inflamed and swollen. This narrows the airway and makes it more difficult to breathe, resulting in wheezing, breathlessness, or coughing. Acute asthma attacks or episodes increase this effect by constricting bronchi muscles and producing excess amounts of mucus. The diameter of the bronchi may decrease to the point that very little air can travel in or out. This causes the affected person to cough and wheeze, feel tightness in their chest, and struggle to breathe. Although the cause is not clear, asthma attacks can occur at any time but are especially frequent at night and in the morning. Severe asthma attacks can be life-threatening, often requiring immediate medical attention.

About 25 million people in the United States have asthma. An estimated 7 million of those affected are children, making asthma one of the most common chronic diseases in children. Before puberty, asthma affects more boys than girls. After puberty, it affects more girls. The condition is more prevalent in urban areas than rural and in those of African and Hispanic descent than in Caucasians. Asthma is not currently preventable or curable, but it is controllable and most people who have it can lead active, relatively normal lives.

Diagram of the Respiratory System, including the Lungs.Source: National Cancer Institute

The exact cause of asthma is unknown, but it is a complex interaction of different factors. The underlying problem seems to be the release of inflammatory molecules by cells in the lining of the bronchi in response to various stimulators or triggers. The triggers for asthma attacks will be slightly different for each person. Some of them are as follows:

Asthma is separated into four categories based on the severity and frequency of a person's symptoms. These categories include mild intermittent, mild persistent, moderate persistent, and severe persistent. Those with mild intermittent asthma may only have occasional episodes and no symptoms at other times. Those with severe persistent asthma may require multiple daily medications to control their condition.

Other lung diseases and conditions such as emphysema and infections can have symptoms similar to asthma, co-exist with asthma, and/or exacerbate asthma. Non-pulmonary conditions such as GERD (gastroesophageal reflux disease, also called acid reflux) can trigger or worsen asthma attacks in some people.

The goals with initial testing are to diagnose asthma and evaluate its severity. Testing may be performed to distinguish asthma from other conditions that cause similar symptoms and to identify the presence of conditions, such as allergies, that have the potential to trigger or worsen asthma attacks. The goals with continued testing are to monitor lung function and asthma control, evaluate and resolve asthma attacks, and identify and address complications and side effects that arise.

The National Heart, Lung, and Blood Institute (NHLBI) National Asthma Education and Prevention Program (NAEPP) released "Expert Panel Report 3: Guidelines for the Diagnosis and Management of Asthma" in August 2007. These guidelines are intended to help guide the diagnosis and monitoring of those with asthma. They focus on assessing and monitoring asthma, educating people, encouraging them to participate in the management of their condition, controlling environmental factors that can trigger or exacerbate asthma attacks, and the use of medications.

Lung Function Tests and Imaging Studies
These are the primary tests used to diagnose, assess, and monitor asthma.

Asthma diagnosis
The NAEPP guidelines recommend:

A detailed medical history and physical exam, focusing on the chest and respiratory tract

Spirometry to evaluate narrowed or obstructed airways (FEV1; Forced Expiratory Volume in 1 second). This test measures the amount and rate of air exhalation as a person blows out through a tube. It can be performed on people 5 years of age or older to demonstrate airway obstruction that is reversible or partially reversible with a short-acting bronchodilator.

"Challenge" tests that provoke the bronchi to constrict (Bronchial Provocation tests), such as exercise, cold air, methacholine, or histamine.

Other pulmonary function studies and/or a chest x-ray

Additional testing as required to help rule out other diagnoses or causes of the symptoms, such as cystic fibrosis, lung infections including tuberculosis, and gastrointestinal reflux

Asthma assessment and monitoring

Spirometry – to evaluate lung function

Peak expiratory flow (PEF) determination – measures the ability to push air out of the lungs or how fast air can be exhaled; this test uses a small device called a Peak Flow meter and can be performed by the person at home to monitor lung function.

Pulse oximetry – a noninvasive way to continuously monitor O2 saturation; may be used in an emergency department or hospital to evaluate oxygen status.

Chest x-ray

Exhaled nitric oxide test test (FeNO; fraction of exhaled NO) – measures nitric oxide in exhaled breath; levels increase in the presence of inflammation of the airways, such as in those with asthma, and may rise and fall depending on the effectiveness of anti-inflammatory treatment. While this test may be useful in guiding the management of asthma patients, it is not yet recommended by NAEPP guidelines and so is not widely used.

Laboratory Tests
Laboratory testing is used to help rule out conditions that cause symptoms similar to asthma, to identify allergies, and to help identify and evaluate complications that arise. During severe asthma attacks, testing may be ordered to evaluate and monitor organ function, oxygen levels, and the body’s acid-base balance. Tests include:

Blood testing for allergic sensitivity – blood tests that are specific for the allergen(s) suspected to be causing symptoms, such as dust mites, mold, pet dander, and pollens; may be ordered to help determine asthma triggers.

Blood gases – an arterial blood sample is collected to evaluate blood pH, oxygen, and carbon dioxide; may be ordered when a person is having an asthma attack.

A healthcare practitioner will consider the results of the general tests, medical history, family history, and risk factors for certain diseases as well as the results of a physical examination. Based on these findings, some additional laboratory tests could be done. Other tests that may be occasionally ordered include:

Identify, treat, and resolve where possible conditions that exacerbate asthma and complications associated with asthma or medication side effects

Educate people and have them be an integral part of their treatment

Encourage an active normal lifestyle

Prevention of asthma attacks is a combination of avoiding substances that trigger episodes, having good asthma control, and recognizing and addressing the early signs of an impending attack. For more on this, visit the American Lung Association's (ALA) web page on Managing Asthma.

Asthma treatment is tailored to the individual and depends upon the severity of the person's asthma. Even people with mild intermittent asthma may occasionally have severe acute asthma attacks. Some asthma medications are given to reduce airway inflammation, while others are used to relax muscles surrounding the airways to make breathing easier. Both long-term and short-term asthma controls must be addressed.

Long-acting medications are typically taken on a daily basis to help prevent attacks.

Quick-acting medications are used as needed to provide relief during an asthma attack.

People with asthma should work with their healthcare provider to become educated about and to monitor their or their child's condition and to determine the best medications to treat their asthma over time. They should develop a treatment plan that guides their day-to-day asthma control, guides their actions when an asthma attack occurs, and helps them determine when they should seek medical attention. Healthcare practitioners will take a person's entire clinical picture into account, as well as all of the drugs that the person is taking to determine the best course of treatment. The ALA web site has detailed information on asthma medicines and their use.

Structures of the lungs. Image credit National Heart Lung and Blood Institute

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Structure of the lungs. Image credit: National Cancer Institute

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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used. To access online sources, copy and paste the URL into your browser.

Sources Used in Current Review

2014 August 4 Updated). What Is Asthma? National Heart Lung and Blood Institute [On-line information]. Available online at http://www.nhlbi.nih.gov/health/health-topics/topics/asthma. Accessed 12/5/15.

(2014 November 18 Updated). Learn How to Control Asthma. CDC [On-line information]. Available online at http://www.cdc.gov/asthma/faqs.htm. Accessed 12/5/15.

(2007 August 28). Expert Panel Report 3: Guidelines for the Diagnosis and Management of Asthma. National Heart, Lung, and Blood Institute, National Asthma Education and Prevention Program [On-line guidelines]. Available online at http://www.nhlbi.nih.gov/guidelines/asthma/asthgdln.htm. Accessed on 11/17/07.

Mckenzie, S. and Dundas, I. (2006 April 19). Spirometry in the diagnosis of asthma in children CME. Medscape from Curr Opin Pulm Med 12(1):28-33, 2006 [On-line CME]. Available online at http://www.medscape.com/viewarticle/529087. Accessed on 11/15/07.

(2006 May, Updated). What is Asthma. National Heart Lung and Blood Institute [On-line information]. Available online at http://www.nhlbi.nih.gov/health/dci/Diseases/Asthma/Asthma_WhatIs.html. Accessed on 11/15/07.

American Academy of Allergy Asthma and Immunology (April 6, 2004). Exhaled Nitric Oxide in the Diagnosis of Asthma (online article, accessed January 2008). Available online through http://www.aaaai.org.

National Asthma Education and Prevention Program (NAEPP). Expert Panel Report 3 (EPR3): Guidelines for the Diagnosis and Management of Asthma. Available online at http://www.nhlbi.nih.gov/guidelines/asthma/asthgdln.htm. Accessed Dec 2011.